Sound-reproducing apparatus



' Oct. 20, 1925. 1,557,554

C. M. BOUDETTE scum) ,iafiraonucmq APPARATUS Filed July 21, 1922 Patented Get. 20, 1925a CLAYTON M. BOUDETTE, OF REVERE, MASSACHUSETTS.

SOUNDREPRODUCING APPARATUS.

- Application filed July 21, 1922. Serial No. 576,539.

To all whom it may concern:

Be it known that I, CLAYTON. M. BOU- nn'rrn, a citizen of the United States, re-

siding at Revere, in the county of Essex and State of Massachusetts, have invented certain new and useful Improvements in 'Sound Reproduc1ng Apparatus, ot which the following is a specification.

This invention relates to sound reproducing apparatus and is especially concerned with the problems presented in the volume reproduction of sounds transmitted by radio telephony.

In radio work itis now a. common practice to use so-called loud speakers in reproducing music, speeches and the like.

.l Vhile these pieces of apparatus give very satisfactory reproductions under some conditions, they produce very distorted re sults at other times and they give only very faint and scarcely audible reproductions under many circumstances.

It is the chief object of the present invention to devise a loud speaking apparatus which will reproduce music, speech, or other sounds truthfully, preserving the original quality and tone. lVnile the in- 'vention isespeoially concerned with loud speaking apparatus designed for use in radio telephony, it can also be used to advantagein other sound reproducing apparatus.

The invention especial-1y involves improvements in the electro-magnetic mech anism of loudspeakers and it utilizes the weak fluctuating voice currents that must be dealt with in wireless receiving apparatus, or in the amplifiers used with them, in a. manner which enables these currents to produce finer gradations in the vibrations of the receivingdiaphragm and to cause thisdiaphragm to respond more accurately to the fluctuations in said currents than do the forms of apparatus in use at the present time.

The nature of the invention will be readily understoodfro n the following description when read in connect-ion with the accompanying drawings illustrating the preferred form'of the invention, and the novel features will be particularly pointed out in the appended claims.

In the drawings, Figure 1 is a perspective View of an electro-magnetic apparatus for vibrating a diaphragm 1414 secured to the plates 55.

Fig. 2 is a cross sectional plan View of the armature of the apparatus shown in F 1g. 1, show ng the mounting of this armature;

Fig. .3 is a vertical cross sectional view of the apparatus shown in Fig. l, the plane of cross section lying in the axis, about which the armature oscillates; and

Fig. 4 is a view, partly in side elevation and partly in vertical cross section, showing the apparatus illustrated in Fig. 1 connected with a diaphragm. p

- The embodiment of the invention illustrated in the drawings comprises four permanent magnets of the horseshoe type design-ated, respectively, at 1, 2, 3 and l, the magnets 1 and 3 being arranged above the respective magnets 2 and 4, and the poles of all four magnets being located closely adjacent to each other. supported in this relationship by metal strips 5-5, preferably of copper, brass, or other suitable non-magnetic material secured to the inside faces of the magnets and provided with out-turned tongues or $0 lugs (S'6 which project between the adjacent faces of the superposed magnets and hold them in properly spaced relationship. Screws 77 threaded into a base'p'late 9 and having collars 8-8 that bear on the 35 upper edges of the uppermost magnets- 1 and 3, serve to clamp all four magnets securely on said base plate, this plate also being made of brass or other suitable nonmagnetic material. slotted, as shown at 1010, to breakup their continuity and to prevent eddy currents from circulating in them.

Mounted between the poles of the pernianent magnets is an armature 12 preferably consisting of a: relatively thin flat plate of silicon steel or other suitable material, this armature being pivoted at its ends, as shown at 13-13, Fig. 2, in metal yoke pieces armature has a length approximately equal to the width of the horseshoe magnets, audit is provided at one corner with a lug 15 which projects beyond the lateral faces of the magnets 3 and ti, and connected by i'neans ot' a rod 16 with the central portion of. a resilient diaphragm 17. The marginal portion of this diaphragm isclainped with even marginal pressure. as usual, between two rubber rings 1S18 located in an anuular recess formed in the lower part of the base plate 9, therings being held in this The magnets are' The plates are 90 This 0 recess by a plate 19 secured to the base 9 by screws -20. The'dia-phragm preferably is made of mica, and the supporting means just described leaves the circular central area of this diaphragm free to vibrate, as

usual in apparatus of this type. The rod" 16 is not connected exactly to thege'omet- -rical center-ofthe diaphragm, but this connection is slightly decentered, the geometrical center of the diaphragm being indicated in Fig. 4, at 22. This highly important and' novel mode of securing the armature rod to" the diaphragm is not claimed herein since it forms the subject-matter of a divisional application- Ser. No. 655,779, filed Aug. 4:,' 1923. e plate 19 is provided with a hollownipple 3 located opposite the central portion of the diaphragm 17, tm which equivalent devicemay be.

nipple a horn or connected I I The mounting of the'armature 12 as above described enables it to oscillate about the axis of the pivots 13-43, but its connection with the resilient diaphragm 17 holds it northe purpose mally in a neutral'or ce-ntral'position. 'For of oscillating this armature about its axis, it is encircled by a coil 25, the plane of the windings of this coil lying at right angles to the axis 1 313 of the armature. A suitable shell of insulating material, arts of which are shown at 26, supports t e coil in.a stationary position between the permanent magnets. I I

The coil is connected in the circuit in which the fluctuating voice currents are induced, and consequently when such currents,

flow througlrit, it produces a correspondingly fluctuating magnetic flux in the armature 12, the magnetic lines of force flowing longitudinally through the armature I from one end thereof'to the other,'parallel to the axis 13-43. This results in producing north and south polesin said armature at opposite ends thereof. Due to the fact that the armature is-flat and relatively wide, north and south poles. are formed at both sides of the axis of the armature. 1

Referring to Figs. 1 and 4, it willbese-en that the north poles of the permanent magnets 2 and 3, (indicated by the letters N-N) are arranged in diametrically opposed relation'ship to each other, while thesou'th poles of the magnetic 1 and 4 (indicated by the; letters S-S) are arranged in a similar re- .lationship. Obviously, the same pole arrang einent exists at the opposite sidepf the .apparatus, the only difi'erence being that the poles are reversed. So long as no-current flows in the coil 25 the poles ofthe permanent magnets will exert: a -s ubstan-, tially balanced action on the armature 12. As soon, however, as a current fiowsthrou'gh' the coil 25, this condition willim'mediately be disturbed. Assuming, for the moment,

that the direction of fiow of current in the coil 25 is suchastocre'zite a north poleat the upper end of the armature 12, Fig. 2, and

a south pole at the opposite end, it-will be evident that in\Fig. 4: the soutlnpole is at the end towardfit he bbserver. Thedeft-hand side of the .armature will beirepelledby the south pole of the magnetsIai d' attracted by the north; pole bf the magnet 2, while theright-hand side of this end of the armature will be attracted by the north pole of the magnet 3' andrepelled by the south poleof the magnet l5. The magnetic forces willoperate in .a similarjnanner: oirthe north pole of the armature at its opposite end, and these forces thus will act, when this condition ob-. tains, to tip the-arghaturlQJn achunterclockwise direction-+ Fig. 4,- about its axis '13-13. The force of thistipping movement will vary wittntlie of the current flowing through thefcoil I -5.When1the-current dies down therilient diaphragm 11 will return the armature. again to'its neutral position If the curreniireverses inthe eoi1s 25, the armature 12 will be tipped in aclockwise direction, Fig. .4. I 9 It will now be; appreciated that with this arrangement very feeble" currents fiowing through the coil 25 will produce relatively powerful oscillations. ofthe armature 12.

These osci lations 'will beaPQsitively trans- 5 .mitted to the diaphragm 17 through the rod tions varying with the fluctuations of the r current in the coil 25.

It will be observed that the facesof the D magnets are cutaway-in a manner whichbling the armature to have? very substantial range of oscillatian. The learance between the tips'of the pole faces and the armature may vary in accordance with-the. amount of input current which willydetermine the clearance, or air gap, required at the outer I edges of the armature. For inanu'facturing purposes it is found to be generally. satisfactory to provide an air gap of fifteenthousandths of, an inch at the outer edges of the armature, this gap'being'sufiicient to permit as great a degree ofoscilla-tion as is ordinarily employed in the use of the ap parat'us. The preferred construction of'the apparatus provides, a ratio of the width of 16, thus producing in thediaphragm'vibra- I i air gap at the outer edge of the armature but that the use of and at the tips of the magnets of five to one, so that with fifteen-thousandths at the armature outer edge the gap can readily be reduced to as low as three-thousandths at the tips of the poles. As illustrated; the relative angular position of the magnets is determined and maintained by properly proportioning the height of the various spacing lugs 6, but it is-within the scope of the invention .to substitute for these lugs a mounting that will permit a relative adjustment vertically of the magnets in a manner more rapidly to accommodate the apparatus to variations in the amount of input current than is possible by changing the length of the lugs 6. It will be observed that the clearance gradually increases as the pole pieces rccede, at either side, from the axis of oscillation of the armature until the maximum air gap, required at the armature outer edges for the amount of input current used, is obtained.

This arrangement has the important prac-' tical advantage of materially increasing the sensitiveness of the instrument, because, by virtue of the decreased air gap at the tips of the poles, the weaker fluctuating current will create a greater displacement of the armature that will, in turn, be transmitted to the diaphragm. The smaller air gap at the pole tips reduces the resistance 'to the passage otmagnetic lines of force so that the weaker fluctuations in current produce greater variations in magnetic flux thus drawing the armature further out of balance. As a result the armature vibrations follow more accurately the variations in current intensity and the sensitivity is increased to such a marked degree that all tone modulations are made distinct and even overtones, as from a piano, are brought out and heard with the original tones that produce them.

It will be understood from the foregoing that the advantages obtained are not dependent upon the use of permanent magnets, electro-magn'ets for oscillating the armature, and thus vibrating the diaphragm, is within the scope of the invention. j

I have found in actual practice that this apparatus reproduces music. speech, and the like. transmitted by radio, clearly and faithfully and is far superior to prior forms ofappa atus of this character of which I have been able to learn. The difference is particularly marked where a volume reproduction of the transmitted sounds is made.

It will be clear to those skilled in the art to which this class of apparatus pertains, and with the general objects of the present invention in view, that changes may be made in the details of structure, the described and illustrated embodiment thereof being intended as an exploitation of its underlying essentials, the'features whereof are definitely stat d in their true scope in the claims herewith.

Having thus described my invention,

What I desire to claim as new is: 1. In a soimd reproducing apparatus, the

combination of an armature, means supporting said armature for oscillating movement about an axis, a coil encircling said armature' and operative when a current flows therethrough to create north and south magneticpoles in said armature with said poles adjacent, respectively, to the opposite ends and. operative when. a current flows therethrough to create noi hand south magnetic poles in said armature with said-poles'adjacent, respectively, to the opposite ends of said axis, means for creating magnetic fields cooperating with said magnetic poles to exert both magnetic attraction and repulsion on said armature at each side oi said axis and thereby to oscillate said armature as the field in said armature fluctuates, and a resilient diaphragm connected with said armasaid armature to be vibratedthereby.

3. In a sound reproducing apparatus, the combination of an arn'iature, means supporting said armaturefor oscillating movement about an axis, a coil encircling said armature and operative when a current flows therethrough to create northand south magnetic poles in said armature with-said poles adacent, respectively, to the opposite ends of said axis, means for creating magnetic lields cooperating withsaid magnetic poles to 05- cillate said armature about said axis when a fluctuating current flowsthrough said coil, and a resilient diaphragm connected with said armature to be vibrated thereby.

4;. In a sound reproducing apparatus,the combination of an armature, means supporting said armature for oscillating movement about an axis, a coil encircling said armature and operative when a current flows therethrough to create north and south magnetic poles in said armature withsaid poles adjacent, respectively, to the opposite ends of said axis, means operative'to create mag-- netic fields exerting attraction and repulsion on said armature at each side of the axis thereot'at each of said poles and thereby to oscillate said armature about its axis as the current in'said coil fluctuates, and a re silient diaphragm connected with said armature to be vibrated thereby 5. In a sound reproducing apparatus, the

j tively associated each side of said axis,

. ing movement about an axis,

lating movement about an axis,

combination of a relatively flat armature,

means supporting said armature for oscillat ing movement about an axis,-a coil operawith said armature and 0pfluctuating current flows create a fluctuating magnet;

' the magnetic flux erative, when a therethrough, to field in said armature with running through the armature substantially,

parallel to said axis, whereby north and south magnetic poles are created in' said armature at opposite ends tl 1ereof,--a plu rality of magnets cooperating with the poles of said armature to exert both magnetic repulsion and attraction on said armature at and a resilient dia-' phragmconnected with said armature to be vibratedthereby.

6. Ina sound reproducing apparatus, the combination of a. relatively fiat armature, means supporting said armature for oscil1ata coil operativel associated with said armature and operative, when a fluctuating current flows therothrou 'h, to create a fluctuating magnet field in said armature with. the magnetic flux running throu h the armature, substantially parallel to said axis, whereby north and south ,-magnetic poles are created in said armatureat both sides of saidaxis, and four permanent. horseshoe magnets arranged two on each side of said axis,

opposite sides of said armature and the north and south poles of the opposite magnets being diametrically opposed to each other, and a resilient diaphragm connected with said armature-at one side of its axis, whereby the, movements of said armature are transmitted to said diaphragm.

7. In a sound reproducing apparatus, the combination of a relatively flat armature, means supporting said armature for oscila coil operatively associated with said armature and operative, when a fluctuating current flows therethrough, field in said armature with the ma netic flux running through the armature stantially parallel to said axle, whereby horth ano south magnetic poles are created in said armature at both sides of said axis, four per manent horseshoe magnets arranged two on each side of said axis, the poles of each magnet being positioned closely adjacent to opposite sides of said armature andholding the armature in substantially a magnetically balanced condition so long as no current is flowing in said coil, a resilient diaphragm, and a positive connection between said diaphragm and. said armature whereby movements of said armature are transmitted f the faces of said perma nent magnets adjacent to said armat urebe,- ing positioned toafford the poles of each' magnet being positioned closely adjacent to to create a fluctuatingmagnet to said diaphragm,

reater clearance with the outer edges of sand armature than with the portions thereof adjacent to its axis.

8, In a sound reproducing, apparatus, the combination of an armature, means support-i ing said armature for oscillating movement about an axis, a coil associated with said armature and operative when a current flows polarize said armature, a

therethrough .to pluralityof m agnets at each side of said axis cooperating with the poles of said armature to exert bothmagnetic repulsion and attraction on the armature at each side-of said' axis, and, a resilient diaphragm connected to said armature to be vibrated thereby.

9. In a sound reproducing apparatus, the

--combination'of, a relatively flat armature;

means supporting said armature for osc llating movement about an axis;

when a fluctuating current .flows therethrough, to create afluctuating magnetic tips of the poles adjacent to said axis, said faces being inclined with reference to said armature and having a'minimum clearance with the armature adjacent to saidv axis and a gradually increasing clearance as tl1eyex tend away from said axis, and a resilient diaphragm connected with said armature to be vibrated thereby.

10. In a sound reproducing apparatus, the combination of a relatively flat armature; means supportin said armature for oscillating movement a out an axis: a coil encircling said armature and operative, when a fluctuating current flows therethrough, to create a fluctuating magnetic field in said armature; meansincludingpole pieces located closely adjacent to the opposite faces of said armature for creating magnetic fields cooperating with said fluctuating field to exert both magnetic attraction and repulsioIrin said armature. the faces of said pole pieces diverging relatively to said armature asthey extend away from said axis, whereby a minimum clearance is provided between them-and the armature adjacent to said axis and said clearance increases as the distance from said axis increases; and a resilient diaphragm connected with said armature to be vibrated thereby.

' CLAYTON M. BOUDETTE.

a coil assomated with said armature and operative, 

